Among other things, coordinate measuring machines (“CMMs,” also known as surface scanning measuring machines) measure geometry and surface profiles, or verify the topography of known surfaces. For example, a CMM may measure the topological profile of a propeller to ensure that its surface is appropriately sized and shaped for its specified task (e.g., moving a 24 foot boat at pre-specified speeds through salt water).
To that end, conventional CMMs typically have a base directly connected with and supporting a movable assembly having a probe that directly contacts and moves along a surface of an object being measured. The base also may support the object being measured. Commonly, the movable assembly forms an air bearing with a rail to permit movement along the rail—i.e., in a direction that is generally parallel with the longitudinal axis of the rail. If the air gap of the air bearing is not consistent, then the probe can move relative to the object. Undesirably, this movement can significantly skew the results of the measurement, particularly when measuring to the micron level.